#!/bin/sh --指定执行脚本的shell；
#第一部分：变量初始化部分：
- # If you change base dir, you must also change datadir. These may get
# overwritten by settings in the MySQL configuration files.
# 指定mysql安装程序及数据目录的路径，一般默认是/usr/local/mysql，但是生产上不建议这么搞；
basedir=/mysql/app/mysql
datadir=/mysql/data/3306/data
- # Default value, in seconds, afterwhich the script should timeout waiting
# for server start.
# Value here is overriden by value in my.cnf.
# 0 means don’t wait at all
# Negative numbers mean to wait indefinitely
# 定义mysql服务启动时间的限制，如果超过900秒没有启动，则脚本退出，即启动失败；
service_startup_timeout=900
- # Lock directory for RedHat / SuSE.
# 该目录存放操作系统默认在关闭过程中的一些服务进程的调用的服务，不建议修改（可在/etc/rc.d/init.d/下看到系统所有的服务），系统在关机时，会依次的正常关闭该目录下的进程，不在该目录下的进程会被强制杀掉；
lockdir='/var/lock/subsys'
lock_file_path="$lockdir/mysql"
- # The following variables are only set for letting mysql.server find things.
# Set some defaults
# 指定mysql.pid文件路径：用于判断mysql有没有启动，默认是空的，所以要进行指定，指定后，方便我们监控；
mysqld_pid_file_path=/mysql/data/3306/mysql.pid
# 定义环境变量：
if test -z "$basedir"
-- -Z：判断引号里的值是否为空，空则执行下一步，否则，执行else；
then
basedir=/mysql/app/mysql
bindir=/mysql/app/mysql/bin
if test -z "$datadir"
then
datadir=/mysql/data/3306/data
fi
sbindir=/mysql/app/mysql/bin
libexecdir=/mysql/app/mysql/bin
else
bindir="$basedir/bin"
if test -z "$datadir"
then
datadir="/mysql/app/3306/data"
fi
sbindir="$basedir/sbin"
libexecdir="$basedir/libexec"
fi
- # datadir_set is used to determine if datadir was set (and so should be
# not set inside of the --basedir= handler.)
# 数据集的路径，默认不写，平时用不到；
datadir_set=
#第二部分：函数申明部分：
- # Use LSB init script functions for printing messages, if possible
# 指定lsb函数路径，有些环境该路径下是没有lsb函数的，可能在/etc/init.d/init-functions路径；
lsb_functions="/lib/lsb/init-functions"
--判断lsb函数是否存在，存在就使用lsb脚本打印消息（init-functions文件中的所有shell函数在当前脚本生效），否则就直接输出成功/失败的信息；
if test -f $lsb_functions ; then
. $lsb_functions
else
log_success_msg()
{
echo " SUCCESS! $@"
}
log_failure_msg()
{
echo " ERROR! $@"
}
fi
# 设置path环境变量；/sbin:/usr/sbin:/bin:/usr/bin系统默认的路径，$basedir/bin：mysql bin路径；
PATH="/sbin:/usr/sbin:/bin:/usr/bin:$basedir/bin"
export PATH
# 传脚本运行时的参数：
mode=$1 # start or stop
[ $# -ge 1 ] && shift
other_args="$*" # uncommon, but needed when called from an RPM upgrade action
# Expected: "--skip-networking --skip-grant-tables"
# They are not checked here, intentionally, as it is the resposibility
# of the "spec" file author to give correct arguments only.
case `echo "testing\c"`,`echo -n testing` in
*c*,-n*) echo_n= echo_c= ;;
*c*,*) echo_n=-n echo_c= ;;
*) echo_n= echo_c='\c' ;;
esac
# 参数解析函数（将参数值赋予变量，主要涉及的参数：--basedir、--datadir、--pid-file、--service-startup-timeout）：
parse_server_arguments() {
for arg do
case "$arg" in
--basedir=*) basedir=`echo "$arg" | sed -e 's/^[^=]*=//'`
bindir="$basedir/bin"
if test -z "$datadir_set"; then
datadir="$basedir/data"
fi
sbindir="$basedir/sbin"
libexecdir="$basedir/libexec"
;;
--datadir=*) datadir=`echo "$arg" | sed -e 's/^[^=]*=//'`
datadir_set=1
;;
--pid-file=*) mysqld_pid_file_path=`echo "$arg" | sed -e 's/^[^=]*=//'` ;;
--service-startup-timeout=*) service_startup_timeout=`echo "$arg" | sed -e 's/^[^=]*=//'` ;;
esac
done
}
wait_for_pid () {
verb="$1" # created | removed
pid="$2" # process ID of the program operating on the pid-file
pid_file_path="$3" # path to the PID file.
i=0
avoid_race_condition="by checking again"
while test $i -ne $service_startup_timeout ; do
case "$verb" in
'created')
# wait for a PID-file to pop into existence.
test -s "$pid_file_path" && i='' && break
;;
'removed')
# wait for this PID-file to disappear
test ! -s "$pid_file_path" && i='' && break
;;
*)
echo "wait_for_pid () usage: wait_for_pid created|removed pid pid_file_path"
exit 1
;;
esac
# if server isn't running, then pid-file will never be updated
if test -n "$pid"; then
if kill -0 "$pid" 2>/dev/null; then
: # the server still runs
else
# The server may have exited between the last pid-file check and now.
if test -n "$avoid_race_condition"; then
avoid_race_condition=""
continue # Check again.
fi
# there's nothing that will affect the file.
log_failure_msg "The server quit without updating PID file ($pid_file_path)."
return 1 # not waiting any more.
fi
fi
echo $echo_n ".$echo_c"
i=`expr $i + 1`
sleep 1
done
if test -z "$i" ; then
log_success_msg
return 0
else
log_failure_msg
return 1
fi
}
第三部分：主体执行部分：
- # Get arguments from the my.cnf file,
# the only group, which is read from now on is [mysqld]
# 判断my_print_defaults文件位置；
if test -x "$bindir/my_print_defaults"; then
-- -x：判断目录下文件是否存在，存在则执行，否则，执行else；
print_defaults="$bindir/my_print_defaults"
else
# Try to find basedir in /etc/my.cnf
conf=/mysql/data/3306/my.cnf
print_defaults=
if test -r $conf
then
subpat='^[^=]*basedir[^=]*=\(.*\)$'
dirs=`sed -e "/$subpat/!d" -e 's//\1/' $conf`
for d in $dirs
do
d=`echo $d | sed -e 's/[ ]//g'`
if test -x "$d/bin/my_print_defaults"
then
print_defaults="$d/bin/my_print_defaults"
break
fi
done
fi
# Hope it's in the PATH ... but I doubt it
test -z "$print_defaults" && print_defaults="my_print_defaults"
fi
- # Read defaults file from ‘basedir’. If there is no defaults file there
# check if it’s in the old (depricated) place (datadir) and read it from there
#查找默认的扩展配置文件；
extra_args=""
if test -r "/mysql/data/3306/my.cnf"
then
extra_args="-e /mysql/data/3306/my.cnf"
fi
# 由程序my_print_defaults打印出的参数，用parse_server_arguments进行解析，解析后的值，就是该脚本的整个环境变量；
parse_server_arguments `$print_defaults $extra_args mysqld server mysql_server mysql.server`
# 设置pid文件的路径；
#
# Set pid file if not given
#
if test -z "$mysqld_pid_file_path"
then
mysqld_pid_file_path=$datadir/`hostname`.pid
else
case "$mysqld_pid_file_path" in
--判断：如果$mysqld_pid_file_path值中有/，则表示该值可以表示路径，可直接使用；如果该值中没有/，则把该值设定在一个路径下进行使用；
/* ) ;;
* ) mysqld_pid_file_path="$datadir/$mysqld_pid_file_path" ;;
esac
fi
# mysql服务脚本启动选项；
case "$mode" in
'start')
# Start daemon
# Safeguard (relative paths, core dumps..)
cd $basedir
echo $echo_n "Starting MySQL"
if test -x $bindir/mysqld_safe
-- -x：判断mysqld_safe是否为可执行文件；
then --如果mysqld_safe是可执行文件，则启动mysqld实例；
# Give extra arguments to mysqld with the my.cnf file. This script
# may be overwritten at next upgrade.
$bindir/mysqld_safe --defaults-file=/mysql/data/3306/my.cnf --datadir="$datadir" --pid-file="$mysqld_pid_file_path" $other_args >/dev/null &
wait_for_pid created "$!" "$mysqld_pid_file_path"; return_value=$?
# $：在shell中用于获取后台运行的pid的进程id，具体的id就是mysqld_pid_file_path文件里对应的value值；!：在mysqld_safe启动mysql实例后，调用$参数；
# Make lock for RedHat / SuSE
# 判断目录$lockdir是否可写，如果可写，就创建一个文件路径，-w：写；
if test -w "$lockdir"
then
touch "$lock_file_path"
fi
exit $return_value
else
log_failure_msg "Couldn't find MySQL server ($bindir/mysqld_safe)"
fi
;;
# mysql服务脚本停止选项；
'stop')
# Stop daemon. We use a signal here to avoid having to know the
# root password.
# 判断mysqld_pid_file_path文件长度是否为0，-s：长度；
if test -s "$mysqld_pid_file_path"
then --若mysqld_pid_file_path文件长度不为0，则创建一个关机的文件；
# signal mysqld_safe that it needs to stop
touch "$mysqld_pid_file_path.shutdown"
mysqld_pid=`cat "$mysqld_pid_file_path"`
# cat：获取mysqld_pid_file_path文件的pid = mysql的进程id；
# 判断进程mysqld_pid是否正常运行，正常运行执行then，否则，执行else；
if (kill -0 $mysqld_pid 2>/dev/null)
then
echo $echo_n "Shutting down MySQL"
kill $mysqld_pid
# mysqld should remove the pid file when it exits, so wait for it.
# 僵尸进程：父进程死掉，子进程仍运行；
# 在正常的情况下，kill进程是可能会出现问题的；一般用kill是用来终止有问题的进程，然后，把进程的资源释放掉；
# 然而，一个进程启动了子进程的话，它只kill父进程，子进程仍运行，这个时候可能会出现问题，所以，mysql在检查pid后，用wait_for_pid检查进程是否是在存活之前退出的；
wait_for_pid removed "$mysqld_pid" "$mysqld_pid_file_path"; return_value=$? --防止僵尸进程，确保在杀死父进程之前，先杀死所有的子进程；
else
log_failure_msg "MySQL server process #$mysqld_pid is not running!"
rm "$mysqld_pid_file_path"
fi
# Delete lock for RedHat / SuSE
# 判断文件$lock_file_path是否存在，存在就清掉；
if test -f "$lock_file_path"
then
rm -f "$lock_file_path"
fi
exit $return_value
else
log_failure_msg "MySQL server PID file could not be found!"
fi
;;
# mysql服务脚本重启选项；
'restart')
# Stop the service and regardless of whether it was
# running or not, start it again.
if $0 stop $other_args; then
$0 start $other_args
else
log_failure_msg "Failed to stop running server, so refusing to try to start."
exit 1
fi
;;
# mysql服务脚本重加载选项；
'reload'|'force-reload')
# 判断$mysqld_pid_file_path文件长度是否为0，不为0，执行then，为0，则执行else；
if test -s "$mysqld_pid_file_path" ; then
read mysqld_pid < "$mysqld_pid_file_path" -- <:赋值，后面的参数赋给前面的参数；
kill -HUP $mysqld_pid && log_success_msg "Reloading service MySQL"
# -HUP：发送挂起信号，大多数服务器进程进行复位操作，并重新加载配置文件；
touch "$mysqld_pid_file_path"
else
log_failure_msg "MySQL PID file could not be found!"
exit 1
fi
;;
# mysql服务脚本状态选项；
'status')
# First, check to see if pid file exists
if test -s "$mysqld_pid_file_path" ; then
read mysqld_pid < "$mysqld_pid_file_path"
# kill -0：不是杀进程，而是起到判断的作用，判断进程$mysqld_pid是否存在，存在则执行then，不存在，则执行else；
if kill -0 $mysqld_pid 2>/dev/null ; then
log_success_msg "MySQL running ($mysqld_pid)"
exit 0
else
log_failure_msg "MySQL is not running, but PID file exists"
exit 1
fi
else
# Try to find appropriate mysqld process
# 通过mysqld来获取pid；
mysqld_pid=`pidof $libexecdir/mysqld`
# test if multiple pids exist
pid_count=`echo $mysqld_pid | wc -w`
if test $pid_count -gt 1 ; then -- -gt：大于；
log_failure_msg "Multiple MySQL running but PID file could not be found ($mysqld_pid)"
exit 5
elif test -z $mysqld_pid ; then -- -z：判断是否为空，为空则执行then；
if test -f "$lock_file_path" ; then --判断路径是否存在，存在则执行then；
log_failure_msg "MySQL is not running, but lock file ($lock_file_path) exists"
# 如果mysql报锁文件存在，则应删除$lock_file_path文件，否则mysql起不来；
exit 2
fi
log_failure_msg "MySQL is not running"
exit 3
else
log_failure_msg "MySQL is running but PID file could not be found"
exit 4
fi
fi
;;
# 脚本其它选项；
*)
# usage
basename=`basename "$0"`
echo "Usage: $basename {start|stop|restart|reload|force-reload|status} [ MySQL server options ]"
exit 1
;;
esac
exit 0